GBE: Try expire some register before register allocation
GBE: Try expire some register before register allocation

1. This would free unused register asap, so it becomes easy to allocate
   contiguous registers.

2. We previously met many hidden register liveness issue. Let's try
   to reuse the expired register early. Then I think wrong liveness may
   easy to find.

Signed-off-by: Ruiling Song <286a174c1339c6eff91abc41c3a1012c95030c95@intel.com>

wdv4758h/beignet,zhenyw/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet,wdv4758h/beignet,freedesktop-unofficial-mirror/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet,zhenyw/beignet,zhenyw/beignet,wdv4758h/beignet